1. Field of the Invention
The present invention relates to a compound semiconductor light emitting diode (LED), and more particularly, to an alternating current (AC) LED having full-wave light emitting cells and half-wave light emitting cells.
2. Discussion of the Background
Compound semiconductor light emitting diodes (LEDS), e.g., GaN-based LEDS, are widely used for display elements and backlights. Further, these LEDs have less electric power consumption and a longer lifespan as compared with conventional light bulbs or fluorescent lamps, so that their application area has been expanded for general illumination to substitute for conventional incandescent bulbs and fluorescent lamps.
An LED is repeatedly turned on/off depending on a direction of current under AC power. Therefore, when the LED is directly connected to an AC power source, there is a problem in that the LED may not continuously emit light and may be easily damaged due to reverse current.
To solve such a problem, an LED (chip) that can be directly connected to a high-voltage AC power source is disclosed by SAKAI et al. in U.S. Patent Application Publication No. 2005/0253151, filed on Aug. 28, 2003, entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS”. Further, AC LEDs having various structures are being developed.
According to U.S. Patent Application Publication No. 2005/0253151, LEDs are two-dimensionally connected through bonding wires in series on a single insulating substrate, such as a sapphire substrate, to form LED arrays. Such two LED arrays are connected to each other in reverse parallel on the substrate, so that light is continuously emitted in response to power supplied from an AC power supply.
According to U.S. Patent Application Publication No. 2005/0253151, one of the LED arrays operates during one half cycle of AC power, and the other array operates during the other half cycle of the AC power. That is, half of the light emitting cells in an LED operate until is a phase of the AC power is changed. Therefore, the use efficiency of the light emitting cells does not exceed 50%.
Meanwhile, an LED is disclosed in U.S. Patent Application Publication No. 2008/0017871, in which a bridge rectifier is formed on a substrate using light emitting cells and an array of serially connected light emitting cells is disposed between two nodes of the bridge rectifier so that the LED operates under AC power. Accordingly, the array of light emitting cells connected to the bridge rectifier emits full-wave light regardless of changes in phase of AC power, so that the use efficiency of light emitting cells can be increased.
However, as the number of light emitting cells connected to the bridge rectifier is increased, high reverse voltage is applied to a specific light emitting cell in the bridge rectifier, and therefore, the light emitting cell in the bridge rectifier is damaged. As a result, the LED may be damaged. To prevent such a problem, the number of light emitting cells in the array of light emitting cells connected to the bridge rectifier may be decreased. However, in this case, it is difficult to provide an LED operating under high-voltage AC power. On the other hand, the reverse voltage can be decreased by increasing the number of light emitting cells connected to the bridge rectifier. However, the use efficiency of light emitting cells is accordingly lowered.